Last week, one of the most important organizations in this industry, SAE International — formerly known as the Society of Automotive Engineers — was in downtown Detroit for the WCX Leadership Summit.

I only wish I could have given those thousands of engineers a homework assignment before they left the Motor City. That’s because automakers, dealers and consumers need a uniform, objective standard with which to measure — and more importantly communicate — an estimate of the remaining battery health of electric vehicles.

EVs will continue to increase their share of new-vehicle sales, which means that in just a few years, they will do the same in the secondary market. But accurately assessing the value of a used EV for a trade-in or consumer purchase requires at least some advanced information about the battery pack, the EV’s most important system and the one whose future service life will depend not only on how far it has been driven but how and even where it was recharged.

Why is this important? The Inflation Reduction Act includes a used-EV purchase credit of up to $4,000 or 30 percent of the transaction price, whichever is lower. Battery packs are the most expensive part of EVs, and replacement costs can reach five figures.

Of course, the industry doesn’t have such a standard now for assessing internal combustion engines or powertrains. But what it does have is the general guidance provided by the odometer and knowledge born of generations of experience gathered while evaluating combustion vehicles.

These are guides rather than standards, and as such, are far more subjective and prone to deviation than would be a repeatable measurement of remaining battery health.

The good news: There are folks already starting to work on the issue, including those in private industry and at the Department of Energy’s National Renewable Energy Laboratory in Golden, Colo. But like with most questions of a technologically advanced nature, getting the right answer is complicated — and it will involve math.

The laboratory has already developed an initial step in the process, its Battery Lifetime Analysis and Simulation Tool, or BLAST. It takes into account a battery pack’s chemistry, its thermal management, charging and ambient temperature profiles based on location. It’s a predictive model, though — explaining really what the battery pack’s likely level of degradation is or should be, instead of what it actually is in that vehicle. BLAST also trips up on being able to communicate that information in something approaching a simple metric.

On the private industry side, Geotab is working from a fleet management standpoint to build its own database for EV performance, tracking long-term battery changes.

Charlotte Argue, the company’s senior manager for sustainable mobility, said making comparisons across different automakers and nameplates is complicated by the lack of a standard.

“Having a standardized battery health diagnosis that all vehicles adhere to and report on could help, with a diagnostic on total capacity, which is tracked over time,” Argue wrote in response to an emailed question. “Even this may not tell the whole story. Some automakers do over the air updates to increase or decrease access to battery capacity — with built-in buffers. So, an (over-the-air) update could make the capacity suddenly appear to improve, or get worse.”

To me, what’s needed is a device that could interface with the EV’s battery port, measure its total battery capacity, current level of charge and highlight any deviations from its initial energy capacity level or ability to fully recharge at maximum rated rates. Then the results have to be boiled down and communicated clearly in a format that’s measurable, much like the EPA’s fuel economy ratings.

So there’s the assignment, engineers and regulators: We need something akin to a Monroney label for used EVs, showing a measurement of the vehicle’s current battery health, perhaps based on a 1-to-100 scale.

Get to it.